APPENDIX TO CHAPTER LIV.
A few illustrations of shrinkage and blow holes
which the author gave, with other subjects, in a lecture before the students of Cornell University, December 14, 1900, and published in the Sib ley Journal of Mechanical Engineering, January and February, 1901, are presented here, as they contain illustrations that are important to be treated in connection with the subject of expansion, shrinkage, etc.
When a shrink hole or holes occur in a casting they will always be found in the part or parts which solidify last. To prevent such holes in castings, we must provide means to fill the void space with metal. It is often difficult and again it is impractical to do so. The chances for such holes occurring are often due to the design. There are times when, if the constructing engineer or designer thoroughly understood the cause of shrink holes and their remedy, he could design or proportion his castings to avoid such evils. The question might be asked, how is a person to know which will be the last part or parts of a casting to solidify, or where we may expect the shrink holes? Such holes will always be found in the upper cast part of uniform solid castings, as seen at E in sample No. 18, Fig. 80, and in the body of heavy sections having light ones joining them, as at F, sample No. 19; that is, if in both cases such bodies are not fed with additional metal to feed the shrinkage. Where light parts join heavy oness to insure equal action in recording* tin* expansion and contraction at. each end of the bar. At f> is a recess, which gives guide to mala,1 the same in the mould, so that in pouring the bars lt open-sand," the metal will ** flow off" at this point when it comes tt> that level, and thereby insure all burs being1 east eioselv to the same thickness.of ^